REACTION OF THIOCARBOXYLIC ACIDS WITH CONJUGATED AZOALKENES

Thiocarboxylic acids smoothly attack conjugated azoalkenes at room tem perature to give hydrazone 1,4-adducts that exhibit tautomerism with t he corresponding enamino forms. These adducts when treated with sodium hydride in tetrahydrofuran at room temperature lead to 1-alkoxycarbon yl- or arbonyl-3-methyl-4-acylthio-1H-pyrazol-5(2H)-ones. The same add ucts in chloroform with trifluoroacetic acid under reflux produce 1-al koxycarbonyl- or inocarbonyl-3-methyl-4-acylthio-5-alkoxypyrazoles. In acidic media with aqueous tetrahydrofuran the 1,4-adducts undergo hyd rolysis affording 2-acylthio-3-oxobutanoate derivatives that exhibit e nol-keto tautomerism. The 1-alkoxycarbonyl- and ocarbonyl-3-methyl-4-a cylthio-1H-pyrazol-5(2H)-one derivatives in methanol under reflux unde rgo solvolysis to give, after a few minutes, simple 3-methyl-4-acylthi o-1H-pyrazol-5(2H)-ones and after a few hours, 4,4'-dithiobis(3-methyl -1H-pyrazol-5(2H)-ones), while 1-alkoxycarbonyl- and aminocarbonyl-3-m ethyl-4-acylthio-5-alkoxypyrazole derivatives are resistant to the sam e reaction conditions even over several days. X-Ray diffraction studie s of some 1-alkoxycarbonyl- and carbonyl-3-methyl-4-acylthio-1H-pyrazo l-5(2H)-ones have been performed in order to determine the structure o f the pyrazole ring in all such compounds, as well as the conformation al situation in the solid state of the substituents on N-1. These inve stigations confirm the reconsideration of the structure assignments fr equently recurring in the literature for some 5- and 3-hydroxypyrazole s.